Automatic door opener



April 21, 1959 w. BORNEMANN AUTOMATIC DOOR OPENER 4 Sheets-Sheet 1 FiledMarch 25. 1955 IN V EN TOR.

W. BORNEMANN v AUTOMATIC DOOR OPENER April 21, 1959 4 Sheets-Sheet 2Filed March 25. 1955 i I N V EN TOR. Val/fizz fiofzzejzzczzzzz BY Wig;

April 21, 1959 w. BORNEMANN AUTOMATIC DOOR OPENER 4 Sheets-Sheet 3 FiledMarch 25. 1955 INVENTOR. Z 15am fiOJJZJZZCUZZ) W. BORNEMANN AUTOMATICDOOR OPENER April 21, 1959 4 Sheets-Sheet 4 Filed March 25. 1955 I v INV EN TOR. f/zam fiorzzemarzzz v/w/Z BY United States Patent AUTOMATICDOOR OPENER William Bornernann, Elmhurst, Ill., assignor to LiftronCorp., Franklin Park, 111., a corporation of Illinois Application March25, 1955, Serial No. 496,694

9 Claims. (Cl. 268-59) The present invention relates to door openingdevices and particularly to manually and electronically controlledelectrically driven operators for heavy doors or gates such as thoseused for garages, shipping docks and fireproof barriers, either hingedor moved along tracks.

The principal object of the invention is to provide a door operator thatis simple in construction, simple in opfiration and easily installed bythose unskilled mechanica y.

A further object is to provide a readily adjustable arrangement by whicha surge of door opening power is available to overcome snow packedagainst it or a heavy initial door movement load, yet will stoptemporarily from operating upon closing without damage to any articleswhich might obstruct the closing.

A further object of the invention is to provide a door operator which isrendered temporarily inoperative if abused or played with over a timegreater than that required to perform several cycles of operation sothat the motor will not be burned out nor anything injured that might bepresent in the path of the door.

The invention is further characterized by an arrangement in which thedirection of movement of the door is automatically reversed whenobstructed so that the next succeeding actuation of the motor, even by aperson who is excited, will move the door away from the obstruction toclear it.

The operation of the invention also avoids the possibility that amanually controlled switch can be held closed continuously to accomplishprolonged operation of the door operating device.

A further object of the invention is to provide a manual means which iseffective temporarily to attain the full thrust of the motor momentarilywhen starting the door operating device.

These being among the objects of the invention, other and furtherobjects will become apparent from the drawings, the description relatingthereto and the appended claims.

In the drawings,

Fig. 1 is a perspective view showing the preferred embodiment of theinvention installed, ready for operation in opening and closing asectional garage door that travels upon tracks;

Fig. 2 is an enlarged sectional view taken upon the line 2-2 in Fig. 1;

Fig. 3 is a side elevational view of the element shown in Fig. 2;

Fig. 4 is an enlarged sectional view of a portion of the embodimentshown in Fig. 1;

Fig. 5 is a section taken upon line 55 of Fig. 4;

s Fig. 6 is a section taken upon line 6 of Fig. 3;

Fig. 7 is a schematic line diagram of the circuit controlling theoperation of the preferred embodiment;

Fig. 8 is a sectional view similar to that of Fig. 2 illustratinganother embodiment of the invention;

Fig. 9 is a diagrammatic view of the self-reversing motor switch forminga part of the motor construction;

2,883,182 Patented Apr. 21, 1959 Fig. 10 is a section through the manualcontrol switch shown in Fig. 1;

Fig. 11 is a side elevation of the invention installed in alternateposition; and

Fig. 12 is an enlarged section taken at one end of the device shown inFig. 11.

The invention contemplates a rotatable worm shaft with a segmented geardisposed in mesh therewith to apply an opening and closing force upon aslidably mounted garage door. The shaft rotates at motor speed (1750r.p.m.) for fast operation of the door, and is supported againstwhipping in an extruded housing. Reversing the direction of the rotationof the worm provides for the opening and closing movements of the door.The worm shaft is also mounted for axial movement in opposite directionsin its housing as opposed by compression springs. A self-reversing motoris employed to drive the shaft and once started in a predetermineddirection, will continue rotation in that direction as powered through aself-energizing relay until the load on the worm shaft compresses one ofthe springs enough to open a switch in the field circuit of the relay.

Referring now to the drawings in greater detail, a sectional garage door10 is shown as mounted by rollers 11 to roll upwardly and horizontallyon tracks 12. A torsion spring 13 balances the weight of the door asapplied through reels 14 having lift lines 15 connected to the bottom ofthe door by bracket 16. The fioor 17 of the garage limits the downwardmovement, whereas stops 18 upon the tracks 12 or upon the worm housinglimit the upward movement of the door. A handle 19 upon the doorprovides means for raising and lowering the door manually, if desired.

Just above the uppermost level of the door in its openingmovement ismounted a horizontally disposed extrusion 20 whose section is best shownin Fig. 5, same comprising a vertical flange portion 21 and acylindrical depending portion 22 slotted longitudinally of its lengthalong the bottom as at 23. A threaded worm shaft 24 is journalled withreasonably close tolerances in the cylindrical portion 22 againstwhipping when rotated at high speed and a slidably mounted follower 25mates with the outer cylindrical surface of the lower portion 22 toslide therealong from one end of the extrusion 20 to the other.

The follower 25 is made up of three elements bolted together. The twooutermost elements engage the depending cylindrical portion 22 and havebolted between them a rack member 27 whose gear teeth 28 mesh with theworm threads 30 upon the worm shaft 24. Below the rack 27 the twoelements 26 extend far enough down to provide a throat between them toreceive the upper end of a tie bar 31 in pivotal relationship upon asmooth shank spacer bolt 32. Thus, as the worm shaft 24 is rotated, thefollower 25 is moved along the extrusion from one end to the otherdepending upon the direction of rotation.

The lower end of the tie bar 31 is secured to the top of the door by abracket 33 in releasable engagement by a removable pin 34.

The upstanding flange portion 21 of the extrusion is perforated alongits length and suspension brackets 35 are employed to support theassembly against forces having a downward component.

Above the door and mounted upon the lintel thereof is a bracket 40which, as more particularly shown in Fig. 2,

3 ears 45 and 46, this arrangement being useful for a purpose laterdescribed.

The outer end of the bracket 40 is cylindrical in form and counterboredas at 4022 longitudinally to receive loosely therein stop washers 48 and50 and the outer race 51a of a ball bearing 51 having an external groove52 therein. The ball bearing 51 including the bearing balls 51b and theinner race 51c supported thereby is held equidistance from the stops 48and 50 by compression springs 53 and 54. O-rings 49 of synthetic rubberare located on opposite sides of the bearing to engage the wall of thecounterbore 40a as forced outwardly by washers 49a between each of themand the respective springs 53 and 54.

The inner race 51c of the ball bearing receives the reduced end of adrive member 55 which is fastened to the worm shaft 24 by the cross-pin56. The outer end of the drive member 55 is flared as at 57 to securethe inner race and the drive member 55 rigidly together. Thus the drivemember, the inner race and the worm shaft turn together as a unit.

The outer stop 50 is held in place by the end 60 of the extrusion beyondwhich the end of the bracket is slotted as at 61 through ears 62a toreceive the flange of the extrusion therebetween in rigid relationshipas held by the bolt 59.

With the construction described thus far, it will be seen how the wormshaft is supported for rotary movement in the cylindrical portion of theextrusion 26 without danger of its whipping when rotating at high speed.Yet it can move when forced to do so in either axial direction againstthe springs 53 or 54 through the ball bearing 51 and the drive member 55that joins the two together. When the screw member moves in either axialdirection, the outer race 51a moves with it.

An aperture 61a in the wall of the cylindrical portion of the bracketexposes the groove 52 of the bearing 51 so that a switch rod 62 slidablymounted upon the bracket by elements 63 will follow the movement of thebearing through a finger 64 engaging in the groove 52.

As more particularly shown in Fig. 3, adjustable cam members 65 and 66are secured to the switch rod 62 by set screws 67 and 68 respectivelywith the cam surfaces 70 and 71 movable with the switch rod along pathsinterfering with the button 72 of a conventional normally closedmicroswitch 73 mounted upon the bracket by screws 74. This arrangementoperates to open the microswitch 73 whenever the switch rod 62 is movedfar enough in either direction that either one of the cams 7t] and 71depress the button 72.

The drive member 55 is driven through a flexible shaft 80 and frictionclutch 81 by self-reversing motor 82. The motor 82 is identified as aself-reversing motor because its alternate starting windings are underthe control of a two position switch 130 rotatable about said motor axisbetween fixed points, and which opens in an axial direction as the motorreaches full speed as the centrifugal elements 1311 move outwardly. Akeyway arrangement 132 holds the switch in either one of its twopositions until the body 133 clears the key 134 as the elements 131centrifugate. Then, once cleared, the body 130 is rotated by its inertiato its other position and the second keyway 132a is ready to engage thekey and close in the new position when the motor slows up and stops, andthe centrifugal elements 131 yield to springs 135 for that purpose. Asthe armature makes its last two or three revolutions the starting switchis then closed in its alter.- nate position by axial movement of thebody 130 in which it places the starting windings of the motor forrotation in the opposite direction in contact with each otherpreliminary to the next time that the motor is again energized.

The operation of the device as described thus far is as follows:

The motor 82 having stopped in a door closing direction has its startingwindings set for rotation in an opening t 4 direction. Then whenever themotor is energized, it will rotate the friction clutch 81, flexibleshaft 80, and the worm shaft 24 in the direction carrying the followeralong the extrusion 20 to pull the top of the door 10 upwardly andrearwardly through the link 31. As the door opens, the torsion spring 13will assist the motor in bearing the weight of the door. When the doorreaches its raised limit as determined by the stops 18, the strain uponthe worm shaft 24, now opposed by the follower 25 being held stationary,will cause the spring 54 to be collapsed and the continued rotation ofthe worm shaft causes the worm shaft to be moved in that direction. Theball bearing 51 will carry the switch rod 62 rearwardly to bring the cam70 in contact and depress the switch button 72 to break the supply ofcurrent to the motor relay. Thereupon the motor will stop and thestarting windings for starting the motor in reverse direction will beclosed. The strain upon the worm shaft being relieved by the stopping ofthe motor, the ball bearing 51 will recover itself enough for theengagement between the cam 70 and the switch button 72 to be terminated.The tension exerted on the O-rings by the compressed spring will causethe O-ring to press radially outwardly against the inner Wall of thecounterbore 46a and snub out any tendency of the worm shaft to chatteror bounce longitudinally under load and cause a false actuation of theswitch button 72. The greater the tendency to compress one of thesprings 53 or 54 with inertias of starting loads, the greater thecompression of the corresponding O-ring and the greater the snubbingtendency thereof to prevent longitudinal bounce between springs 53 and54.

Thereafter when the motor is again energized, it will rotate thearmature in the opposite direction and correspondingly the worm shaft 24to move the follower 25 in the opposite direction driving the link 31 ina direction forcing the door to close. When the door is fully closed, astrain is developed upon the worm shaft in the opposite direction undercontinued rotation of the motor, the spring 53 will be compressed, theswitch bar 62 moved in the direction opposite to its previous movementand the cam 71 will engage the switch button 72 to open the circuitcontrolling the motor. The starting switch of the motor is againreversed.

Referring now to Fig. 7, the schematic circuit controlling energizationof the motor is illustrated wherein the motor 82 is under the control ofthe normally open switch of a relay 91 as powered with 110 AC.electrical current through leads 92. The other switch 93 of the relay isa self-energizing switch for the relay 91 and is connected in serieswith a normally open manual switch 94 and the microswitch 95. A 40 ohmresistor 95a is included to control the safety cut-out switch or circuitbreaker. In parallel with the switches 93 and 95 is a circuit whichincludes the coil 96 of the relay and a 15 volt source of transformerpower which is so indicated.

This last circuit also includes a safety circuit breaker of novel design97 which will be described shortly.

When the manual switch 94 is closed, the field coil 96 of the solenoid91 is energized through the last-mentioned circuit a to d inclusive.Energization of the coil 96 closes the switch 93 and the switch 90. Theswitch 90 starts the motor whereas the switch 93 sustains energizationof the coil 96 through the microswitch 95 and the safety breaker 97.This circuit is identified by the letters e, f, b, g, 11. Thus, wheneither the microswitch 95 or the overload switch 97 is opened, the coil96 is de-energized and the motor switch 90 drops out to stop the motor.

Connected in parallel with the manual switch 94 and supplementing itsoperation is a switch 100 of a relay 101 powered from a radio receiver102. The radio receiver is pretuned to receive a signal sent momentarilyfrom a transmitter carried by the automobile or any other device such asfire alarm broadcast whose opera- .5 tion is intended to ultimatelyculminate in a closure or opening of the door.

Referring now to the overload safety device same includes a bimetal 103subjected to the heat of a heater 104 when energized quickly by theclosure of a circuit which includes a manual switch 94 and a switch 105controlled by the bimetal 103, or very slowly while the motor isrunning. The first circuit includes the leads a, b, g, h, while thesecond circuit 2, f, b, g, h, includes the coil 96 and switch 93, whichif on too long will be shut off as as a safety precaution.

As shown in Fig. 10, the power plug-in and the switch 94 are formed in asingle unit as molded in soft rubber so that prongs 110 can be insertedin the convenience outlet 111 (Fig. 1) and a third wire through the cord112 leads to the switch blade of the switch 94 which is actuated by aninsulated button 113. With this arrangement, the entire device can bemounted according to the units as shown in the lower set of broken linesof Fig. 7 with the extension cord plugged into a convenience outlet toprovide not only a connection with the house current but also a switchfor manually starting the motor either to open or close the door.

The embodiment shown in Fig. 8 is one which essentially substitutes acombination drive and compression spring 120 as a substitute for theflexible drive 80 and the compression springs 53 and 54, a mountingelement 121 carrying switch control elements 65 and 66 operated by ballbearing 51 as hereinbefore described. With the single spring 120 notonly is the shaft 24 rotated but the spring 120 itself will accommodateaxial movement of the shaft for purposes of actuating the microswitch 73or any other kind of normally closed switch. The drive shown in Fig. 8may or may not include the friction clutch 81. As shown the frictionclutch is not included.

A better understanding of the significance of the arrangement of theelements can be had from a detailed consideration of the adjustments andthe flexibility of operation available with the device described.

If it is assumed that the door might be extra heavy or of another type,requiring extra power to start movement of the door, as where in winterit might be snowed in from the outside, the operator can press and holdthe button 113 of switch 100. This will prevent any opening of themicroswitch aflecting the operation of the motor because the manualswitch 94 continues to energize the relay. Thus the full power of themotor within the limits of the frictional clutch 81 is applied to startthe opening of the door. However, if the holding of the switch 100continues too long, the heater 104 heats up the bimetal to deflect in adirection opening switch 89 and breaking the circuit d, e, f, whereuponthe coil 96 is de-energized to open the motor switch 90. The motorcannot then be started again until after the bimetal has cooled off infive or six seconds and the switch 89 again closed. If the load is toomuch for the system to carry, the motor 82 will turn but the clutch 81will slip to avoid possible damage to the operating parts.

However, if the door is consistently hard to start, the cam 70 can beadjusted to provide a greater distance of travel for the switch bar 62before the button 72 of the microswitch 73 is contacted. Thus the spring54 has to be compressed more before the microswitch is opened and thisadjustment thereby determines the amount of energy that is applied tomove the door without holding the switch 100 closed any length of time.In this connection, it is to be noted that the energy to raise the doorshould be set at a higher level than that required to close the door.Thus the closing cam stop 71 is adjusted closer to the button 72 so thatslight resistance to the closure of the door will compress the spring 53to open the microswitch 72. Then when anything is 6. under the door, andthe device has been tested with a persons hand resting there, no damageis done. In fact, an automobile can be left halfway outside the garagewith the door open and somebody press the switch 113 accidentallywithout doing any damage to the automobile.

Another feature of the invention resides in the fact that when theflexible shaft is used the motor can be located above the ceiling of thegarage or any other place either on the right hand side or the left handside wherever desired, it being preferred to have the outlet of theradio plugged into the control box mounted on the back end of the motorso that the motor can be reached any place it is located by a plug-inconnection from the radio to not only supply the control, but also thepower for the motor.

In those instances where the tracks upon which the door moves areinclined tracks, the extrusion support 20 should also be inclined. Thusonce the bolt 42 is mounted to secure the bracket 41 in place againstthe door lintel, the bolt 44 being left out, the extrusion 20 can belocated at any inclination desired through the flexing of the spring 43.Thereafter once the position of the extrusion 20 is determined theoverlapping ears 45 and 46 can be drilled to provide coincident openingsand the bolt 44 inserted and tightened in place to clamp the bracket 40in its proper position.

Also, provision has been made in the invention that in the event ofpower failure in a community when the owner wishes to open his garagedoor, a key can be used to remove a trap door a near the bracket 33.Through the opening thus provided the bolt 34 can be withdrawn to permitthe door to be opened. Turning of a key releases shot bolts 121a byretracting them in much the same manner that the door of a safe isunlocked and opened.

The installation of the embodiment of the invention is particularlyeasy, it coming within the do-it-yourself category for those unskilledmechanically. The base 41 is located and the lag bolt 42 used to holdthe bracket in position. Thereafter the extrusion is inserted and boltedin place with brackets 35 installed to provide the correct height. Thebolt 44 is then applied and the overhead construction is completed. Thebracket 33 is attached to the garage door and the tie 31 fastened withthe runner 25 located as near to the bracket 40 as practical. The motoris then mounted a measured distance radially from the bolt 42 and theflexible shaft is attached by set screw 123 to the drive member 55. Theradio 102 is then mounted and plugged into the motor and the leadin cord112 taken to a convenience wall outlet and plugged in. The device isready for operation. If the owner desires or has special problems withhis particular door, the adjustment of the cam faces 70 and 71 withrespect to the button 72 can be made according to simple instructionsand the door is in operation as desired by the owner himself inaccordance with the adjustments made by the owner.

Another method of installation makes it possible for the deviceembodying the invention being usable with every type of lift door andbuilding conditions. In Fig. 11 where the ceiling clearance ispractically nothing, the installation is turned end for end and theotherwise free end of the extrusion is mounted on the lintel by abracket with a boss 141 received in the end of the extrusion. The motoris then mounted on the ceiling by a drop beam 142 arrangement.

Having thus described the invention and two of its embodiments, it willbe apparent how the objects stated are attained and how various andfurther changes can be made without departing from the spirit of theinvention, the scope of which is commensurate with the appended claims.

What is claimed is:

1. An automatic door operator comprising an elongated tubular supporthaving a longitudinally extending slot through one wall of the tubularsupport, a worm shaft journalled in said tubular support for relativeaxial movement therebetween, resilient means urging said shaft andsupport to maintain a predetermined relative axial position, a motor forrotating said shaft in alternate directions of rotation between stops,follower means slidably mounted upon said support including a rack inmesh with said shaft through said slot to place an axial thrust loadupon said shaft absorbed by said resilient means, and means forcontrolling said motor including a relay having two normally openswitches one in circuit with the motor, the other in a second circuitwhich includes the coil of the relay, a switch in a third circuit inparallel with the second circuit for energizing the coil of the relayand including a thermal overload cut out actuated only when said switchin the third circuit is closed, a normally closed switch in series withsaid other switch in said second circuit for stopping said motorwhenever said shaft and support move predetermined distances withrespect to each other from said predetermined position in oppositedirections.

2. An automatic door operator comprising a tubular support member havinga slot along the bottom side and a hanger flange along the top side, abracket supporting one end of the tubular member, a ball bearing withthe outer race slidably mounted with respect to said tubular member insaid bracket, a worm shaft carried by the inner race of said ballbearing and journalled in said tubular member for relative axialmovement with respect to said tubular member, resilient elements onopposite sides of said ball bearing in said bracket urging said bearingand shaft to a predetermined axial position, a follower slidable on saidtubular member and meshing in driven relationship with said shaftthrough said slot, a motor for rotating said shaft in a predetermineddirection of rotation, means for connecting said follower to a door tobe operated, and switch means carried by bracket for stopping saidmotor, a switch bar slidably mounted on the bracket engaging saidbearing to be controlled by movement of said bearing axially againstsaid resilient means, and means carried by said switch bar for engagingsaid switch means when said switch bar is carried by said bearing apredetermined distance.

3. In combination a support defining a cylindrical wall and having aslot along one side a shaft having a helical thread therein journalledin the support upon the cylindrical wall for relative axial movement, afollower slidable on said support including a rack gear meshing with theshaft through said slot, a reversible electric motor driving said shaft,means for reversing said motor each time the motor stops, means forstarting the motor including a relay having a self-energizing switch,means for closing said switch, normally closed switch means connected inseries with said self-energizing switch, and means operated by axialmovement of said shaft for opening said normally closed switch means tode-energize said relay.

4. In a door operating mechanism the combination of an electric motor, acontrol circuit for the motor, a housing having a cylindricalcounter-bore therein, stop washers disposed loosely in the counterbore,a frictionless bearing slidably mounted for longitudinal movement insaid counterb'ore between the stop washers, compression springs disposedbetween the stop washers and frictionless bearing to hold itequidistance from the stop washers, resilient O-rings disposed onopposite sides of the bearing to engage the wall of the counterbore andsubjected to compression of said springs to compress the O-ringsoutwardly to engage the wall of the counterbore, a worm shaft rotated bysaid motor secured to said frictionless bearing, follower means meshedin drive relationship with said shaft for moving said door, and meansoperable by relative axial movement of the shaft for stopping said motorincluding a switch in said control circuit and a follower carried bysaid shaft shiftable therewith to engage said switch at predeterminedlimits of movement.

5. A door operating mechanism comprising an electric motor, .means forreversing the direction of rotation of the motor each time it stops, aworm shaft connected with said motor mounted for relative axialmovement, a follower driven by said shaft, means connecting saidfollower to a door, a relatively frictionless bearing having an innerrace fixedly secured to said shaft and an outer annular race having saidinner race rotatably mounted therein, a helical spring coaxially mountedon said shaft on each side of said hearing and held in abuttingengagement with said outer race at one end, switch means including amovable switch actuating element engaged by said bearing operable bysaid relative axial movement of said shaft and consequent movement ofsaid bearing for stopping the motor, said helical spring having ahousing providing a stop at each end for engaging the ends of saidspring opposite said first-named ends and an O-ring compressed by saidhelical springs to expand against said housing in frictional engagementtherewith for snubbing axial vibration in said worm shaft.

6. An automatic door operator comprising an elongated tubular supporthaving a longitudinally extending slot through one wall of the tubularsupport, a worm shaft journalled in said tubular support for relativeaxial movement therein, resilient means urging said shaft and support tomaintain a predetermined relative axial position, a member carried bysaid shaft and movable thereby with respect to said support, a motor forrotating said shaft in alternate directions of rotation, means forstopping said motor whenever said shaft and member move with respect tosaid support from said predetermined position in opposite directionsincluding a circuit having a relay with a self-energizing switch meansfor closing said switch, a second switch in series with the coil of therelay, a safety switch in series with the self-energizing switch and thecoil of said relay, said second switch being actuated by said member tode-energize said relay to stop said motor when said member moves apredetermined distance with respect to said support, follower meansslidably mounted upon said support including a rack in mesh with saidshaft through said slot, and means for connecting said follower means toa door to be operated.

7. An automatic door operator comprising an elongated tubular supporthaving a longitudinally extending slot through one wall of the tubularsupport, a worm shaft journalled in said tubular support for relativeaxial movement therein, resilient means urging said shaft and support tomaintain a predetermined relative axial position, a motor for rotatingsaid shaft in alternate directions of rotation at full motor speedincluding a direct drive element interconnecting said motor and shaft,means for stopping said motor whenever said shaft and support movepredetermined distances with respect to each other from saidpredetermined position in either direction including a relay foroperating the motor, circuit means for energizing said relay to startthe motor having a safety switch and a second switch for de-energizingsaid relay, means carried by said shaft for actuating said second switchfor deenergizing the relay when said shaft moves a predetermineddistance with respect to said support, follower means slidably mountedupon said support in mesh with said shaft through said slot, and meansfor connecting said follower means to a door to be operated.

8. An automatic door operator comprising a tubular support memberdefining a cylindrical wall and having a slot along one side, a bearingmember slidably mounted with respect to said tubular member, a wormshaft carried by said bearing and journalled in said tubular member uponsaid wall for relative axial movement with re-. spect to said tubularmember, resilient means urging said bearing to a predetermined position,a follower slidable on said tubular member and meshing with said shaftthrough said slot, a reversible motor for rotating said shaft, means forreversing the motor each time it stops, means for connecting saidfollower to a door to be operated, and switch means for controlling saidmotor actuated by movement of said bearing axially against saidresilient means a predetermined distance including means for startingthe motor including a relay having a selfenergizing switch, means forclosing said switch, normally closed switch means connected in serieswith said self-energizing switch, and means operated by axial movementof said shaft for opening said normally closed switch means todeenergize said relay.

9. In a door operating mechanism the combination of a self-reversingelectric motor, a worm shaft connected with said motor and rotated atmotor speed, a support member having a wall defining a surface ofrevolution journalling said shaft for a major portion of the length ofthe shaft upon said surface of revolution for relative axial movement insaid wall, a slot in said wall along one side exposing said shaft, afollower engaging in mesh with said shaft through said slot andtravelling on said support member, means connecting said follower withthe door to place an axial load upon the worm shaft,

and means operable from the said shaft for cutting ofi the power fromthe motor when the effort to move the door exceeds a predeterminedamount, said last-mentioned means including a resilient elementresiliently supporting said shaft in a predetermined axial position tocushion axial movement of said shaft under said load, a switch rodslidably mounted on said support and moved by relative axial movement ofthe worm shaft, an adjustable cam on said rod and a switch carried bysaid support member engaged by said cam to de-energize said motor.

References Cited in the file of this patent UNITED STATES PATENTS1,833,943 Hill Dec. 1, 1931 1,959,292 Morris May 15, 1934 2,000,515Gross May 7, 1935 2,011,057 Kraft Aug. 13, 1935 2,037,780 Gross Apr. 21,1936 2,253,170 Dunham Aug. 19, 1941 2,407,537 Chapman Sept. 10, 1946

